Boost power conversion circuit, method, inverter, apparatus, and system

ABSTRACT

This application discloses a boost power conversion circuit, a method, an inverter, an apparatus, and a system. In the conversion circuit, a voltage control circuit is added on a three-level boost. The voltage control circuit can be connected in series in a third closed loop, and the third closed loop is a loop including an inductor, a first switching transistor, a flying capacitor, a second diode, and an input end. The voltage control circuit clamps a voltage of a common point of the first diode and the second diode when a voltage on an input end of the boost power conversion circuit is less than a startup voltage of the boost power conversion circuit. The voltage borne by the second diode is reduced, so that a diode with relatively small voltage stress can be selected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2019/115075, filed on Nov. 1, 2019, which claims priority toChinese Patent Application No. 201811573498.5, filed on Dec. 21, 2018.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to the field of power electronicstechnologies, and in particular, to a boost power conversion circuit, amethod, an inverter, an apparatus, and a system.

BACKGROUND

A boost circuit is a boost power conversion circuit, and can boost andthen output an input voltage, to convert power. The boost circuitincludes a two-level boost circuit and a multi-level boost circuit. Thetwo-level boost circuit is usually used in scenarios with a relativelylow voltage level, and the two-level boost circuit has two input levels.The multi-level boost circuit is used in scenarios with a higher voltagelevel, and the multi-level boost circuit can convert power for an inputlevel that is greater than or equal to three levels.

Compared with the two-level boost circuit, the multi-level boost circuitimplements a plurality of levels by improving a topological structure ofthe multi-level boost circuit, to output a high voltage and large power.For a same input voltage, a prominent advantage of the multi-level boostcircuit is that the multi-level boost circuit can reduce voltage stressof a power component. The voltage stress borne by the power component ishalf that of the two-level boost circuit, so that a power component witha relatively low voltage withstand level can be used to implementvoltage output with a relatively high level. In addition, due todifferent modulation schemes, the multi-level boost circuit has smallerinput current ripples than the two-level boost circuit, so that a volumeand design costs of a filter are reduced. Therefore, the multi-levelboost circuit has a broad application prospect.

Application of the multi-level boost circuit is described below by usingthe photovoltaic power generation field as an example.

To improve power generation efficiency of a photovoltaic component, anoutput end of the photovoltaic component is connected to an input end ofthe multi-level boost circuit, and output ends of a plurality ofmulti-level boost circuits are connected in parallel to control theconnected photovoltaic component, so that the photovoltaic component canoutput relatively large power.

However, when the plurality of boost circuits are connected in parallel,an input end of a specific boost circuit may not be connected to thephotovoltaic component, and consequently a voltage is less than astartup voltage of the boost power conversion circuit. In this case,input ends of other boost circuits are connected to an input source, andtherefore, if a bus voltage is set on output ends of all boost circuits,a power component in a boost circuit whose voltage is lower than thestartup voltage of the boost power conversion circuit bears the busvoltage. Therefore, a diode in the boost circuit needs to be of a typewhose voltage stress can bear the bus voltage. Consequently, it isdifficult to select a type of the diode, and in addition, higher voltagestress leads to higher component costs.

SUMMARY

To resolve the foregoing technical problems in the prior art,embodiments of the present invention provides a boost power conversioncircuit, a method, an inverter, an apparatus, and a system, so that whena voltage on an input end of the boost power conversion circuit is lessthan a startup voltage of the boost power conversion circuit, a voltageborne by a diode in the boost circuit can be reduced, and a diode withrelatively small voltage stress can be selected.

According to a first aspect, an embodiment of this application providesa boost power conversion circuit, and a voltage control circuit is addedbased on a three-level boost circuit. The boost power conversion circuitincludes a first switching transistor, a second switching transistor, aninductor, a flying capacitor, a first diode, a second diode, and avoltage control circuit. The inductor, the first diode, and the seconddiode are successively connected in series to form a first branch, thefirst branch is connected in series to an input positive electrode andan input negative electrode of the boost power conversion circuit toform a main circuit, both an anode of the first diode and an anode ofthe second diode are close to the input positive electrode of the boostpower conversion circuit, and both a cathode of the first diode and acathode of the second diode are close to the input negative electrode ofthe boost power conversion circuit. The inductor, the first switchingtransistor, and the second switching transistor are connected in seriesto form a first closed loop, and the first switching transistor, thesecond switching transistor, the first diode, and the second diode forma second closed loop. One end of the flying capacitor is connected to acommon point of the first diode and the second diode, and the other endof the flying capacitor is connected to a common point of the firstswitching transistor and the second switching transistor. The voltagecontrol circuit is connected in series in a third closed loop, and thethird closed loop is a loop including the inductor, the first switchingtransistor, the flying capacitor, the second diode, the input positiveelectrode, and the input negative electrode. The voltage control circuitis configured to make a voltage borne by the second diode less than abus voltage of the boost power conversion circuit, and the bus voltageis a voltage difference between a positive bus voltage and a negativebus voltage; or a first end of the voltage control circuit is connectedto a common end of the first diode and the second diode, a second end ofthe voltage control circuit is connected to a reference point, thereference point is used to provide a clamping potential, and theclamping potential is between a negative bus potential and a positivebus potential. The voltage control circuit is configured to clamp avoltage of the common point of the first diode and the second diode whena voltage on an input end of the boost power conversion circuit is lessthan a startup voltage of the boost power conversion circuit.

The added voltage control circuit can clamp the voltage of the commonpoint of the first diode and the second diode, and make, when thevoltage on the input end of the boost power conversion circuit is lessthan the startup voltage of the boost power conversion circuit, avoltage borne by the common point of the first diode and the seconddiode less than the bus voltage, so that voltage stress borne by thecommon point of the first diode and the second diode can be reduced, andselection of a diode type is facilitated. Costs of a diode are directlyproportional to voltage stress borne by the diode, and higher voltagestress that the diode can bear leads to higher costs.

In one embodiment, the voltage control circuit can be connected inseries in the third closed loop, to divide a voltage of the seconddiode, thereby reducing voltage stress borne by the second diode. Thevoltage control circuit includes one of a clamping diode, a controllableswitching transistor, and a compound component, and the compoundcomponent includes the clamping diode and the controllable switchingtransistor that are connected in parallel.

In one embodiment, because when the voltage control circuit includes thecontrollable switching transistor or the compound component, there isthe controllable switching transistor, and because the controllableswitching transistor cannot automatically perform actions, a controlleris required to control an on/off state of the controllable switchingtransistor, in other words, whether the controllable switchingtransistor is closed or open. The voltage control circuit can furtherinclude a controller. The controller can be configured to: when thevoltage on the input end of the boost power conversion circuit is lessthan the startup voltage of the boost power conversion circuit, controlto open the controllable switching transistor. The controller can befurther configured to: when the voltage on the input end of the boostpower conversion circuit is greater than the startup voltage of theboost power conversion circuit, control to close the controllableswitching transistor.

In one embodiment, when the voltage control circuit includes a clampingdiode, the clamping diode can automatically perform actions, in otherwords, has features of being forward conductive and reversely cut off.Therefore, the controller is not required to control an on/off state ofthe clamping diode. To better divide the voltage of the second diode, aresistor is used to enforce voltage division. In this case, the voltagecontrol circuit may further include a first resistor and a secondresistor. The first resistor is connected in parallel between two endsof the clamping diode, and the second resistor is connected in parallelbetween two ends of the second diode.

In one embodiment, when the voltage control circuit includes thecompound component, the voltage control circuit further includes a firstresistor and a second resistor. The first resistor is connected inparallel between two ends of the clamping diode, and the second resistoris connected in parallel between two ends of the second diode.

In one embodiment, when the voltage control circuit includes thecontrollable switching transistor, to better divide the voltage of thesecond diode, a resistor is used to enforce voltage division. Thevoltage control circuit further includes a controller, a first resistor,and a second resistor. The controllable switching transistor isconnected in series between the first diode and the second diode, thefirst resistor is connected in parallel between two ends of thecontrollable switching transistor, and the second resistor is connectedin parallel between two ends of the second diode.

In one embodiment, to reduce costs and reduce a circuit size, anexisting resource in a current boost can be effectively used to providea clamping potential of the reference point. For example, a buscapacitor is used to provide the clamping potential. In other words, theboost further includes a first bus capacitor and a second bus capacitor.The first switching transistor, the second switching transistor, thefirst diode, the second diode, the first bus capacitor, and the secondbus capacitor form a second closed loop. The reference point is a commonpoint of the first bus capacitor and the second bus capacitor. When acapacitance of the first bus capacitor is equal to a capacitance of thesecond bus capacitor, a voltage of the clamping potential is ½ of thebus voltage.

In one embodiment, to reduce costs and reduce a circuit size, anexisting resource in a current boost can be effectively used to providea clamping potential of the reference point. For example, a buscapacitor is used to provide the clamping potential. In other words, theboost may further include the following four bus capacitors: a first buscapacitor, a second bus capacitor, a third bus capacitor, and a fourthbus capacitor. The first switching transistor, the second switchingtransistor, the first diode, the second diode, the first bus capacitor,the second bus capacitor, the third bus capacitor, and the fourth buscapacitor can form a second closed loop. The reference point is anycommon point between the first bus capacitor, the second bus capacitor,the third bus capacitor, and the fourth bus capacitor. When capacitancesof the first bus capacitor, the second bus capacitor, the third buscapacitor, and the fourth bus capacitor are all equal, locations ofreference points are different, and therefore corresponding clampingpotentials are different. For example, when a common point of the firstbus capacitor and the second bus capacitor is connected, a voltage ofthe clamping potential is ¼ of the bus voltage.

In one embodiment, when one end of the voltage control circuit isconnected to the reference point, the voltage control circuit mayspecifically include a third switching transistor and a controller. Thecontroller is used to control an on/off state of the third switchingtransistor. When clamping is required, the third switching transistor iscontrolled to be closed. When clamping is not required, the thirdswitching transistor is controlled to be opened, in other words, thevoltage control circuit loses effect. Specifically, a first end of thethird switching transistor is connected to the common end of the firstdiode and the second diode, and a second end of the third switchingtransistor is connected to the reference point. The controller isconfigured to: when the voltage on the input end of the boost powerconversion circuit is less than the startup voltage of the boost powerconversion circuit, control to close the third switching transistor. Thecontroller is further configured to: when the voltage on the input endof the boost power conversion circuit is greater than the startupvoltage of the boost power conversion circuit, control to open the thirdswitching transistor.

In one embodiment, when one end of the voltage control circuit isconnected to the reference point, the voltage control circuit mayspecifically include a diode. When clamping is required, the diode playsa conduction role, and when clamping is not required, inverse cut-off ofthe diode does not work. Specifically, the voltage control circuitincludes a third diode. A cathode of the third diode is connected to thecommon point of the first diode and the second diode, and an anode ofthe third diode is connected to the reference point.

In one embodiment, the first branch may be close to an end of the inputpositive electrode, which is specifically: a first end of the inductoris connected to the input positive electrode, and a second end of theinductor is connected to the first diode and the second diode that aresuccessively connected in series.

In one embodiment, the first branch may be close to an end of the inputnegative electrode, which is specifically: a first end of the inductoris connected to the input negative electrode, and a second end of theinductor is connected to the first diode and the second diode that aresuccessively connected in series.

According to a second aspect, an embodiment of this application furtherprovides a boost power conversion circuit control method, applied to theforegoing boost power conversion circuit. The method includes: when itis determined that a voltage on an input end of the boost powerconversion circuit is less than a startup voltage of the boost powerconversion circuit, making, by a voltage control circuit, a voltageborne by a second diode less than a bus voltage of the boost powerconversion circuit, where the bus voltage is a voltage differencebetween a positive bus voltage and a negative bus voltage. When thevoltage on the input end of the boost power conversion circuit is lessthan the startup voltage of the boost power conversion circuit, avoltage borne by a common point of a first diode and the second diode ismade less than the bus voltage, so that voltage stress borne by thecommon point of the first diode and the second diode can be reduced, andselection of a diode type is facilitated. Costs of a diode are directlyproportional to voltage stress borne by the diode, and higher voltagestress that the diode can bear leads to higher costs.

According to a third aspect, an embodiment of this application furtherprovides an inverter. The inverter includes two levels of circuits. Onelevel is the foregoing boost power conversion circuit, that is, directcurrent-direct current (DC-DC). The other level is an inverter circuit,that is, direct current-alternating current (DC-AC). The inverter isused in the photovoltaic power generation field, to be specific, aninput end of the boost power conversion circuit is connected to aphotovoltaic component, to boost and then output an output voltage ofthe photovoltaic component to an input end of the inverter circuit, andthe inverter circuit inverts, into an alternating current, a directcurrent output by the boost power conversion circuit and provides thealternating current to a subsequent-level circuit. The subsequent-levelcircuit may be an alternating-current power network oralternating-current load.

According to a fourth aspect, an embodiment of this application furtherprovides a photovoltaic power generation apparatus, including theforegoing photovoltaic component and the foregoing boost powerconversion circuit. The boost power conversion circuit is in one-to-onecorrespondence with the photovoltaic component. An input end of theboost power conversion circuit is connected to the photovoltaiccomponent. The boost power conversion circuit is configured to boost andthen output an output voltage of the connected photovoltaic component toa subsequent-level circuit. When a voltage on an input end of the boostpower conversion circuit is less than a startup voltage of the boostpower conversion circuit, a voltage borne by a common point of a firstdiode and a second diode is made less than a bus voltage, so thatvoltage stress borne by the common point of the first diode and thesecond diode can be reduced, and selection of a diode type isfacilitated.

According to a fifth aspect, an embodiment of this application furtherprovides a photovoltaic power generation system, including at least twophotovoltaic power generation apparatuses described above. Output endsof boost power conversion circuits in the at least two photovoltaicpower generation apparatuses are connected in parallel. When a voltageon an input end of a boost power conversion circuit in one of thephotovoltaic power generation apparatuses is less than a startup voltageof the boost power conversion circuit, a diode of the boost powerconversion circuit bears a back voltage of a bus voltage of anotherboost power conversion circuit connected in parallel to the boost powerconversion circuit. Therefore, a voltage control circuit can be used toclamp a voltage for a diode, so that the diode bears less voltage stressthan the bus voltage, and selection of a diode type is facilitated.

Compared with the prior art, embodiments of the present invention haveat least the following advantages:

The boost power conversion circuit can include a voltage controlcircuit, the boost power conversion circuit can include a first diodeand a second diode that are connected in series, and both the firstdiode and the second diode are freewheeling diodes. When a voltage on aninput end of the boost power conversion circuit is less than a startupvoltage of the boost power conversion circuit, but there is a busvoltage on an output end of the boost power conversion circuit, thefirst diode and the second diode bear a bus voltage in a reversedirection. Therefore, a voltage of a common point of the first diode andthe second diode needs to be clamped. The voltage control circuit addedin the embodiments of this application can clamp the voltage of thecommon point of the first diode and the second diode, and when thevoltage on the input end of the boost power conversion circuit is lessthan the startup voltage of the boost power conversion circuit, thevoltage borne by the common point of the first diode and the seconddiode is made less than the bus voltage, so that voltage stress borne bythe common point of the first diode and the second diode can be reduced,and selection of a diode type is facilitated.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of thisapplication or in the prior art more clearly, the following brieflydescribes the accompanying drawings required for describing theembodiments or the prior art. Apparently, the accompanying drawings inthe following descriptions show some embodiments of this application,and a person of ordinary skill in the art may still derive otherdrawings from these accompanying drawings without creative efforts.

FIG. 1 is a topological structure diagram of a three-level boostcircuit;

FIG. 2 is a waveform graph of a drive signal when D<0.5;

FIG. 3 is a path graph of a switching mode a when D<0.5;

FIG. 4 is a path graph of a switching mode b when D<0.5;

FIG. 5 is a path graph of a switching mode c when D<0.5;

FIG. 6 is a path graph of a switching mode d when D<0.5;

FIG. 7 is a waveform graph of a drive signal when D<0.5;

FIG. 8 is a path graph of a switching mode a when D>0.5;

FIG. 9 is a path graph of a switching mode b when D>0.5;

FIG. 10 is a path graph of a switching mode c when D>0.5;

FIG. 11 is a path graph of a switching mode d when D>0.5;

FIG. 12 is a schematic diagram of application when output ends of aplurality of boost circuits are connected in parallel in a photovoltaicpower generation system according to an embodiment;

FIG. 13 is a schematic diagram of a boost power conversion circuitaccording to an embodiment of this application;

FIG. 14 is a schematic diagram of another boost power conversion circuitaccording to an embodiment of this application;

FIG. 15 is a schematic diagram of still another boost power conversioncircuit according to an embodiment of this application;

FIG. 16 is a schematic diagram showing that an inductor in a boost powerconversion circuit is connected to an input negative electrode accordingto an embodiment of this application;

FIG. 17a is a schematic diagram of yet another boost power conversioncircuit according to an embodiment of this application;

FIG. 17b is a schematic diagram of a boost power conversion circuitaccording to an embodiment of this application;

FIG. 18 is a schematic diagram of another boost power conversion circuitaccording to an embodiment of this application;

FIG. 19 is a schematic diagram of still another boost power conversioncircuit according to an embodiment of this application;

FIG. 20 is a schematic diagram of yet another boost power conversioncircuit according to an embodiment of this application;

FIG. 21 is a flowchart of a boost power conversion circuit controlmethod according to an embodiment of this application;

FIG. 22 is a schematic diagram of an inverter according to an embodimentof this application; and

FIG. 23 is a schematic diagram of a photovoltaic power generation systemaccording to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

To make a person skilled in the art better understand technicalsolutions provided in embodiments of this application, a workingprinciple of a multi-level boost circuit is described below by using anexample in which the multi-level boost circuit is a three-level boostcircuit.

FIG. 1 is a topological structure diagram of a three-level boostcircuit.

The three-level boost circuit includes a flying capacitor C_(fly),V_(in) is an input voltage, and V_(bus) is a bus voltage on an outputside of the boost circuit, in other words, an output voltage. Both T1and T2 are switching transistors. D1 and D2 are respectively diodes thatare inversely connected in parallel to T1 and T2. D3 and D4 arefreewheeling diodes. L is an inductor. C_(bus) is a bus capacitor on theoutput side of the boost circuit.

Based on a relationship between the input voltage Vin and the outputvoltage C_(bus), the boost circuit separately works in a working mode inwhich a duty cycle D is less than 0.5 and a working mode in which a dutycycle D is greater than 0.5. When V_(in)>0.5Vbus, the duty cycle D isless than 0.5. When V_(in)<0.5V_(bus), the duty cycle D is greater than0.5. On/off states are different in the two modes. Working principles ofthe two modes are separately described below.

(1) D<0.5

When V_(in)>0.5V_(bus), the duty cycle D is less than 0.5. When D<0.5, awaveform graph of a drive signal is shown in FIG. 2, and a currentflowing path in each switching mode is shown FIG. 3 to FIG. 6, where asolid line represents a current path.

T is a switching period, and drive signals of T1 and T2 differ by aphase angle of 180 degrees.

As shown in FIG. 3, when D<0.5, in a switching mode a, T1 is on, T2 isoff, D4 is conducted, and D3 is cut off. Because a voltage V_(Cfly) ofthe flying capacitor is controlled to be 0.5V_(bus), a voltage V_(in)borne by two ends of the inductor L minus 0.5V_(bus) is greater than0.5V_(bus), and a current of the inductor linearly increases. In thiscase, voltage stress of D3 is 0.5V_(bus), the diode D4 is conducted, andthere is no inverse voltage stress.

As shown in FIG. 4 and FIG. 6, when D<0.5, switching modes b and d aretotally the same, and appear twice in a same period. Both T1 and T2 arein an off state. A current of the inductor freewheels by using D3 andD4. D3 and D4 are conducted, and there is no inverse voltage stress.

As shown in FIG. 5, when D<0.5, in a switching mode c, T1 is off, T2 ison, D3 is conducted, and D4 is cut off. Voltage stress of D4 isV_(bus)−V_(Cfly)=0.5V_(bus). According to a voltage-second balanceprinciple for two ends of the inductor, to be specific, in one workingperiod, a product of time and a voltage between two ends of the inductoris 0, it can be learned that

(V _(in) −V _(bus) +V _(Cfly))·DT+(V _(in) −V _(bus))·(1−2D)T+(V _(in)−V _(Cfly))·DT=0

It can be learned by simplifying the formula that

${V_{bus} = \frac{V_{in}}{1 - D}},$

and an output voltage can be controlled by controlling the duty cyclesof T1 and T2.

(2) D>0.5

When V_(in)<0.5V_(bus), the duty cycle D is greater than 0.5. WhenD>0.5, a waveform graph of a drive signal is shown in FIG. 7. WhenD>0.5, a current flowing path in each switching mode is shown in FIG. 8to FIG. 11, where a solid line represents a current path.

As shown in FIG. 8 and FIG. 10, when D>0.5, current flowing paths inswitching modes a and c are totally the same, and the two switchingmodes appear in different phases of one period. T1 and T2 are conducted,and D3 and D4 are cut off. A voltage between two ends of the inductor Lis V_(in), and a current of the inductor linearly increases. Bothvoltage stress of D3 and voltage stress of D4 are 0.5V_(bus).

As shown in FIG. 9, when D>0.5, in a switching mode b, T1 is on, T2 isoff, D4 is conducted, and D3 is cut off. Voltage stress of D3 is0.5V_(bus).

As shown in FIG. 11, when D>0.5, in a switching mode d, D2 is on, D1 isoff, D3 is conducted, and D4 is cut off. Voltage stress of D4 is0.5V_(bus).

Similarly, it can be learned according to a voltage-second balanceprinciple for two ends of the inductor that

$V_{bus} = {\frac{V_{in}}{1 - D}.}$

It can be learned from the foregoing analysis that, in various workingmodes in steady states, both voltage stress of D3 and voltage stress ofD4 are half an output voltage, that is, 0.5V_(bus). A type of a diodecomponent can be selected based on the voltage stress. This is anadvantage of a three-level boost circuit with the flying capacitor.

However, when output ends of a plurality of multi-level boost circuitsare connected in parallel, and a voltage on an input end of one or moremulti-level boost circuits is less than a startup voltage of the boostpower conversion circuit, a bus voltage is set on an output end of aboost circuit whose input end is connected to an input source. Becausethe output ends of all the boost circuits are connected in parallel, adiode in a boost circuit in which a voltage on an input end is less thanthe startup voltage of the boost power conversion circuit bears voltagestress whose magnitude is the bus voltage. Consequently, the diode isdamaged, or otherwise, a type of a component whose voltage stress isgreater than or equal to the bus voltage needs to be selected as thediode.

It should be noted that, one case in which the voltage on the input endof the boost power conversion circuit is less than the startup voltageof the boost power conversion circuit is that the input end of the boostpower conversion circuit is not connected to the input source. Forexample, in the photovoltaic power generation field, the input end ofthe boost power conversion circuit is not connected to a correspondingphotovoltaic component. When the input end of the boost power conversioncircuit is not connected to the input source, the voltage on the inputend of the boost power conversion circuit is less than the startupvoltage, in other words, the boost power conversion circuit cannot bestarted to work.

For example, FIG. 12 is a schematic diagram showing that output ends ofa plurality of boost circuits are connected in parallel in thephotovoltaic power generation field.

An output end of a first boost circuit 100 and an output end of a secondboost circuit 200 are connected in parallel, an input end of the firstboost circuit 100 is connected to a first photovoltaic component PV1,and an input end of the second boost circuit 200 is connected to asecond photovoltaic component PV2. In actual application, one powerstation includes N PVs, and N is a positive integer. For N boostcircuits, a user may configure a connection of each PV at random, and itis possible that one or more PVs are not connected to a correspondingboost circuit. In this case, a diode in a boost circuit that is notconnected to a PV bears a relatively high bus voltage. Still refer toFIG. 1. When output ends of a plurality of boost circuits are connectedin parallel, in other words, the plurality of boost circuits share anoutput bus, if another boost circuit has been powered on, but this boostcircuit is not powered on, there is a bus voltage, and because both avoltage of a flying capacitor and an input voltage of this boost circuitare 0, it can be approximately considered as equipotential between acathode of D3 and an anode of D2. In this case, D4 bears the entire busvoltage Vbus. If a type of D4 is selected based on stress of 0.5Vbus, D4breaks down due to overvoltage.

Therefore, to resolve the foregoing technical problems, this applicationprovides a boost power conversion circuit that includes a voltagecontrol circuit. The boost power conversion circuit includes a firstdiode and a second diode that are connected in series, and both thefirst diode and the second diode are freewheeling diodes. When there isa bus voltage on an output end of the boost power conversion circuit,the first diode and the second diode bear a bus voltage in a reversedirection. Therefore, a voltage of a common point of the first diode andthe second diode needs to be clamped. The voltage control circuit addedin this embodiment of this application may clamp the voltage of thecommon point of the first diode and the second diode, and make, when avoltage on an input end of the boost power conversion circuit is lessthan a startup voltage of the boost power conversion circuit, thevoltage borne by the common point of the first diode and the seconddiode less than the bus voltage, so that voltage stress borne by thecommon point of the first diode and the second diode can be reduced, andselection of a diode type is facilitated.

Circuit Embodiment 1

FIG. 13 is a schematic diagram of a boost power conversion circuitaccording to an embodiment of this application.

The boost power conversion circuit provided in this embodiment includesa first switching transistor T1, a second switching transistor T2, aninductor L, a flying capacitor Cfly, a first diode D1, a second diodeD2, and a voltage control circuit 300.

The inductor L, the first diode D1, and the second diode D2 aresuccessively connected in parallel to form a first branch, and the firstbranch is connected in series to an input positive electrode and aninput negative electrode of the boost power conversion circuit to form amain circuit. The inductor L, the first switching transistor T1, and thesecond switching transistor T2 are connected in series to form a firstclosed loop, and the first switching transistor T1, the second switchingtransistor T2, the first diode D1, and the second diode D2 form a secondclosed loop. One end of the flying capacitor Cfly is connected to acommon point of the first diode D1 and the second diode D2, and theother end of the flying capacitor Cfly is connected to a common point ofthe first switching transistor T1 and the second switching transistorT2.

There are the following two implementations for the voltage controlcircuit 300.

In one implementation, the voltage control circuit is connected inseries in a third closed loop. The voltage control circuit is configuredto make a voltage borne by the second diode less than a bus voltage ofthe boost power conversion circuit. The bus voltage is a voltagedifference between a positive bus voltage and a negative bus voltage, inother words, a voltage difference between Vbus+ and Vbus−.

In the other implementation, a first end of the voltage control circuit300 is connected to a common end of the first diode D1 and the seconddiode D2, and a second end of the voltage control circuit 300 isconnected to a reference point. The reference point is used to provide aclamping potential, and the clamping potential is between a negative buspotential and a positive bus potential. The voltage control circuit isconfigured to: when a voltage on an input end of the boost powerconversion circuit is less than a startup voltage of the boost powerconversion circuit, clamp a voltage of the common point of the firstdiode and the second diode.

It should be noted that the clamping potential may have a same referencepotential as the positive bus potential and the negative bus potential.For example, the clamping potential, the positive bus potential, and thenegative bus potential all use the ground as a reference potential.

The third closed loop is a loop including the inductor L, the firstswitching transistor T1, the flying capacitor Cfly, the second diode D2,and an input source, and is a concave loop formed by dashed lines shownin FIG. 13.

When the voltage on the input end of the boost power conversion circuitis less than the startup voltage of the boost power conversion circuit,the voltage control circuit 300 is configured to clamp the voltage ofthe common point of D1 and D2, so that the voltage of the common pointof D1 and D2 is less than the bus voltage of the boost power conversioncircuit.

The voltage control circuit 300 is configured to: when the voltage onthe input end of the boost power conversion circuit is less than thestartup voltage of the boost power conversion circuit, clamp the voltageof the common point of D1 and D2. If the voltage of the common point ofD1 and D2 is not clamped, because an output end of the boost powerconversion circuit is connected in parallel to another boost powerconversion circuit, and an input end of the another boost powerconversion circuit is connected the input source, a bus voltage is seton the output end. In this case, the bus voltage is exerted on D2, andD2 bears the bus voltage. The voltage control circuit 300 in thisembodiment forcibly clamps the voltage of the common point of D1 and D2at a voltage value that is less than the bus voltage. In this way, D2does not need to bear a relatively high bus voltage, so that voltagestress of D2 is reduced, and selection of a type of D2 is facilitated.

In addition, when the input end of the boost conversion circuit isconnected to the input source, the voltage control circuit 300 may bedisconnected, so that the voltage control circuit 300 loses effect, inother words, does not clamp a voltage of D2. Therefore, normal workingof the boost conversion circuit is not affected.

In specific implementation, the voltage control circuit 300 may includea voltage division component, and divide the bus voltage and then clampdivided voltages on two ends of D2. Alternatively, the voltage controlcircuit 300 may be connected to a reference point, and a clampingpotential of the reference point is between a negative bus potential anda positive bus potential. It may be understood that a smaller clampingvoltage leads to smaller voltage stress borne by D2 and makes it easierto select a type of D2.

Specific implementations of the voltage control circuit 300 areseparately described below with reference to the accompanying drawings.First, a second end of the voltage control circuit 300 may be connectedto a reference point, and a clamping potential of the reference point isbetween a negative bus potential and a positive bus potential. Aspecific value of the clamping potential is not specifically limited inthis embodiment of this application. For example, a voltage of theclamping potential may be half the bus voltage or ¼ of the bus voltage.

Circuit Embodiment 2

FIG. 14 is a schematic diagram of another boost power conversion circuitaccording to an embodiment of this application.

An example in which a voltage control circuit includes at least acontrollable switch is used as an example for description in thisembodiment. The controllable switch may be a relay, a contactor, asemiconductor switch, or a reverse-conducting switching transistor. Thesemiconductor switch includes a metal oxide field-effect transistor oran insulated gate bipolar transistor, and the reverse-conductingswitching transistor includes a metal oxide field-effect transistor or areverse-conducting insulated gate bipolar transistor. When thecontrollable switch is a relay or a contactor, a normally-closed typemay be used, to be specific, when there is no input source, thecontrollable switch is in an on state, and the controllable switch is inan off state when being powered on.

A controller is required to control on/off states of the semiconductorswitch and the reverse-conducting switching transistor. An example inwhich the controllable switch is a third switching transistor S and acontroller is required to control a status of the third switchingtransistor is used below for description.

In this embodiment, for example, the voltage of the clamping potentialis half the bus voltage Vbus, that is, ½Vbus. Generally, a first buscapacitor Cbus+ and a second bus capacitor Cbus− that are connected inseries are connected between an output positive electrode and an outputnegative electrode of the boost power conversion circuit, and acapacitance of Cbus+ is equal to a capacitance of Cbus−, in other words,a middle point voltage of Cbus+ and Cbus− is half the bus voltage Vbus.In other words, a first end of S is connected a common point of D1 andD2, and a second end of S is connected to a common point of Cbus+ andCbus−.

Because the controllable switching transistor cannot automaticallyperform switching actions, the boost power conversion circuit in thisembodiment further includes a controller (not shown in the figure); and

the controller is configured to: when a voltage on an input end of theboost power conversion circuit is less than a startup voltage of theboost power conversion circuit, control to close the controllableswitching transistor S to clamp the power control circuit, in otherwords, clamp a voltage of D2 at ½Vbus. In this way, D2 does not need tobear the entire bus voltage Vbus.

A working principle after S is added is described below.

Before the input end of the boost power conversion circuit is powered on(V_(in)=0), a voltage is set on a bus. For example, output sides of aplurality of boost power conversion circuits are connected in paralleland share a same bus, other boosts have been powered on, but this boostpower conversion circuit has no input voltage V_(in). If S is not added,both V_(Cfly) and V_(in) are 0, T1 is equivalent to beingbidirectionally short-circuited by D3 and D1, and therefore, V_(in), L,T1, T2, D3, and Cfly may all be approximately considered asequipotential. In this case, D2 bears the entire bus voltage V_(bus). Ifa type of D2 is selected based on 0.5V_(bus), D2 breaks down due toovervoltage. After S is added, when another boost is powered on, the busis charged, and at the same time, because S is conducted, a currentpasses through S, Cfly, D3, and an input capacitor to form a chargingloop, thereby ensuring that a voltage on a positive end of Cfly is notless than a negative bus voltage.

The controller is further configured to: when it is determined that theinput end of the boost power conversion circuit is connected to theinput source, control to open S to disconnect the voltage controlcircuit. In other words, when S is opened, the entire voltage controlcircuit does not work, and the entire boost power conversion circuitworks normally.

In FIG. 14, a voltage clamping point connected to a second end of S is½Vbus, and the second end may further be connected to another voltagepoint in addition to ½Vbus, for example, ¼Vbus. Specifically, refer toFIG. 15. Four bus capacitors that are connected in series are connectedbetween an output positive electrode and an output negative electrode ofthe boost power conversion circuit: a first bus capacitor Cbus1, asecond bus capacitor Cbus2, a third bus capacitor Cbus3, and a fourthbus capacitor Cbus4. The first switching transistor T1, the secondswitching transistor T2, the first diode D1, the second diode D2, thefirst bus capacitor Cbus1, the second bus capacitor Cbus2, the third buscapacitor Cbus3, and the fourth bus capacitor Cbus4 form a second closedloop. The reference point is any common point between the first buscapacitor Cbus1, the second bus capacitor Cbus2, the third bus capacitorCbus3, and the fourth bus capacitor Cbus4. In FIG. 15, for example, thereference point is a common point of Cbus3 and Cbus4. When capacitancesof the four bus capacitors are equal, a voltage provided by thereference point is ¼Vbus. In addition, the reference point may beanother reference point in addition to the reference point shown in FIG.15. For example, the reference point is a common point of Cbus1 andCbus2, and a corresponding clamping voltage is ¾Vbus. Certainly, thereference point may also be a common point of Cbus2 and Cbus3, and acorresponding clamping voltage is ½Vbus.

In both FIG. 14 and FIG. 15, locations of the reference point aredescribed as examples, and a voltage corresponding to the referencepoint may alternatively be another value provided that the voltage isless than the bus voltage. This is not specifically limited in thisembodiment of this application.

In addition, both FIG. 14 and FIG. 15 are described by using an examplein which the inductor L is connected to an end that is close to theinput positive electrode. To be specific, the inductor L, the firstdiode D1, and the second diode D2 are successively connected in seriesto form a first branch, and the first branch is connected in series tothe input end of the boost power conversion circuit to form a maincircuit. Specifically,

a first end of the inductor L is connected to the input positiveelectrode, and a second end of the inductor L is connected to the firstdiode D1 and the second diode D2 that are successively connected inseries.

It may be understood that L may be alternatively connected to an endthat is close to the input negative electrode. Specifically, refer toFIG. 16. FIG. 16 is a schematic diagram that corresponds to FIG. 14 andthat shows that L is connected to an end of the input negativeelectrode.

The inductor L, the first diode D1, and the second diode D2 aresuccessively connected in series to form a first branch, and the firstbranch is connected in series to the input end of the boost powerconversion circuit to form a main circuit. Specifically,

a first end of the inductor L is connected to the input negativeelectrode, and a second end of the inductor L is connected to the firstdiode D1 and the second diode D2 that are successively connected inseries.

In the following embodiments, a connection manner of the inductor mayalso be the foregoing two manners. In other words, the inductor isconnected to the input positive electrode of the boost power conversioncircuit or the input negative electrode of the boost power conversioncircuit.

FIG. 14 to FIG. 16 are described by using an example in which a switchincluded in the voltage control circuit is a controllable switchingtransistor. Descriptions are provided below by using an example in whichthe switch is an uncontrollable diode. Due to a unilateral conductionfeature of a diode, a controller is not required to control an on/offstate of the diode, and the diode is automatically conducted or cut offwhen a voltage between two ends of the diode meets a condition.

Circuit Embodiment 3

FIG. 17a is a schematic diagram of still another boost power conversioncircuit according to an embodiment of this application.

A voltage control circuit in the boost power conversion circuit providedin this embodiment includes at least a third diode D5.

An anode of the third diode D5 is connected to a reference point, and acathode of the third diode D5 is connected to a common point of thefirst diode D1 and the second diode D2.

A working principle after S is added is described below.

Before an input end of the boost power conversion circuit is powered on(V_(in)=0), a voltage is set on a bus. For example, output sides of aplurality of boost power conversion circuits are connected in paralleland share a same bus, other boosts have been powered on, but this boostpower conversion circuit has no input voltage V_(in). If D5 is notadded, both a voltage V_(Cfly) of a flying capacitor and the inputvoltage V_(in) are 0, and T is equivalent to being bidirectionallyshort-circuited by diodes D3 and D1. Therefore, V_(in), an inductor L,switching modules T1 and T2, D1, and the flying capacitor may all beapproximately considered as equipotential. In this case, D2 bears anentire bus voltage V_(bus). If a type of D2 is selected based on0.5V_(bus), D2 breaks down due to overvoltage. After D5 is added, whenanother boost is powered on, the bus is charged, and at the same time,because D5 is conducted, a current passes through D5, the flyingcapacitor, D3, and an input capacitor to form a charging loop, therebyensuring that a voltage on a positive end of the flying capacitor is notless than a negative bus voltage.

It should be noted that, in the embodiments corresponding to FIG. 14 toFIG. 17a , the voltage control circuit may further include a resistor.For example, for FIG. 14, the resistor and the third switchingtransistor S are connected in series, and for FIG. 17a , the third diodeD5 may be connected in series to the resistor. A quantity of resistorsis not specifically limited in the embodiments of this application. Oneresistor may be connected in series in the voltage control circuit, or aplurality of resistors may be connected in series in the voltage controlcircuit.

That the second end of the voltage control circuit is connected to thereference point is described in the foregoing embodiments. The followingembodiments show that the voltage control circuit is connected in seriesin a loop and is configured to divide a bus voltage, to clamp a voltageof a common point of D1 and D2.

Circuit Embodiment 4

FIG. 17b is a schematic diagram of a boost power conversion circuitaccording to an embodiment of this application.

This embodiment shows that a voltage control circuit can be connected inseries in any one or more of a plurality of locations in a loop. Forsimplicity, and to reduce components and costs, the voltage controlcircuit may be connected in series in the loop. A specific location inwhich the voltage control circuit is connected in series is notspecifically limited. For example, the location may be locations shownby A1, A2, A3, A4, and A5 in FIG. 17 b.

It should be noted that the voltage control circuit connected in seriesin the loop includes any one of a clamping diode, a controllableswitching transistor, and a compound component, and the compoundcomponent includes a clamping diode and a controllable switchingtransistor that are connected in parallel.

When the compound component further includes controllable switchingtransistors that are connected in parallel on two ends of the clampingdiode or includes the clamping diode and the controllable switchingtransistor that are connected in parallel,

the voltage control circuit further includes a controller.

The controller is configured to: when a voltage on an input end of theboost power conversion circuit is less than a startup voltage of theboost power conversion circuit, control to open the controllableswitching transistor, or otherwise, control to close the controllableswitching transistor.

In FIG. 17b , A1 to A5 are forms in which a diode and a controllableswitching transistor are connected in parallel. In actual application,many controllable switching transistors have an antiparallel diode, andsuch a controllable switching transistor can be directly used as thevoltage control circuit. It may be understood that a direction in whicha current passes through the diode is a direction in which a current ina loop.

Descriptions are provided below by using an example in which the voltagecontrol circuit is connected between D1 and D2.

FIG. 18 is a schematic diagram of still another boost power conversioncircuit according to an embodiment of this application.

A voltage control circuit in the boost power conversion circuit providedin this embodiment includes a clamping diode D6, a first resistor R1,and a second resistor R2.

An anode of the clamping diode D6 is connected to a cathode of the firstdiode D1, and a cathode of the clamping diode D6 is connected to ananode of the second diode D2.

The first resistor R1 is connected in parallel between two ends of theclamping diode D6.

The second resistor R2 is connected in parallel between two ends of thesecond diode D2.

A working principle of this embodiment is described below.

When a voltage on an input end of the boost power conversion circuit isless than a startup voltage of the boost power conversion circuit, a busvoltage Vbus is exerted on a series loop including R1 and R2, and R1 andR2 divide the voltage. Therefore, a voltage borne by D4 corresponds to adivided voltage of R2, and a voltage on R2 is less than the bus voltage,so that the voltage borne by D4 can be reduced. Certainly, a smallervalue of R2 and a larger value of R1 lead to a smaller voltage borne byD4. However, because D6 is also a diode, a voltage on R1 is a voltageborne by D6. Therefore, for unified selection of diode types, aresistance of R1 may be equal to a resistance of R2, in other words, R1and R2 equally divide the bus voltage. However, the resistance of R1 andthe resistance of R2 may alternatively be unequal.

It should be noted that, in the solution provided in this embodiment,when the voltage control circuit is A4 or A5, the voltage controlcircuit is not only applicable to a case in which the voltage on theinput end of the boost power conversion circuit is less than the startupvoltage of the boost power conversion circuit, but is also applicable toa case in which the input end is reversely connected to an input source,to be specific, a case in which a positive electrode and a negativeelectrode are reversed. However, implementations of A1 to A3 are onlyapplicable to a case in which the voltage on the input end is less thanthe startup voltage of the boost power conversion circuit.

Circuit Embodiment 5

The embodiment corresponding to FIG. 18 includes the clamping diode D6.Because D6 is connected in series in a main circuit, to be specific,when the input end of the boost power conversion circuit is connected toan input source, a current passes through D6 when D6 is conducted, and acurrent loss of the diode is relatively large. Therefore, power energyis wasted, efficiency is reduced, and photovoltaic power generationefficiency is reduced especially in the photovoltaic power generationfield. To reduce a loss of D6, a switch may be further connected inparallel between two ends of D6. When the input end of the boost powerconversion circuit is connected to the input source, the switch that isconnected in parallel to D6 is controlled to be closed, to short-circuitD6, so that a current does not pass through D6. Therefore, a powerenergy loss caused by conduction of D6 can be avoided. Detaileddescriptions are provided below with reference to the accompanyingdrawings.

FIG. 19 is a schematic diagram of still another boost power conversioncircuit according to an embodiment of this application.

A voltage control circuit provided in this embodiment further includes acontroller (not shown in the figure) and a fifth switching transistor S.The fifth switching transistor S is connected in parallel between twoends of the clamping diode D6.

The controller is configured to: when it is determined that the voltageon the input end of the boost power conversion circuit is less than thestartup voltage of the boost power conversion circuit, control to openthe fifth switching transistor S, and is further configured to: when itis determined that the input end of the boost power conversion circuitis connected to the input source, control to close S.

In this embodiment, when the input end of the boost power conversioncircuit is connected to the input source, S is controlled to be closed,so that D6 and D2 are connected in series, and R1 and R2 divide the busvoltage. D6 bears a voltage divided by R1, and D2 bears a voltagedivided by R2. Therefore, voltage stress borne by D2 can be reduced, andD2 is prevented from bearing the bus voltage alone. When the input endof the boost power conversion circuit is connected to the input source,a voltage of D2 does not need to be clamped. Therefore, S may becontrolled to be closed, to short-circuit D6. Therefore, a current doesnot pass through D6, and a power energy loss caused when a currentpasses through D6 can be avoided.

Circuit Embodiment 6

In both the embodiment corresponding to FIG. 18 and the embodimentcorresponding to FIG. 19, a fourth diode is included. In the followingdescriptions, no fourth diode is included, and a voltage of the seconddiode is clamped by using a controllable switch and a voltage divisionresistor.

FIG. 20 is a schematic diagram of another boost power conversion circuitaccording to an embodiment of this application.

A voltage control circuit provided in this embodiment further includes acontroller (not shown in the figure), a fifth switching transistor S, afirst resistor R1, and a second resistor R2.

S is connected in series between the first diode D1 and the second diodeD2.

The first resistor R1 is connected in parallel between two ends of thefifth switching transistor S.

The second resistor R2 is connected in parallel between two ends of thesecond diode D2.

The controller is configured to: when it is determined that a voltage onan input end of the boost power conversion circuit is less than astartup voltage of the boost power conversion circuit, control to openS, and is further configured to: when it is determined that the inputend of the boost power conversion circuit is connected to an inputsource, control to close S.

When the voltage on the input end of the boost power conversion circuitis less than the startup voltage of the boost power conversion circuit,voltage stress of D2 needs to be reduced. Therefore, in this case, R1and R2 need to be opened, so that R1 and R2 divide the voltage. Voltagestress borne by D2 is a voltage divided by R1, and the voltage dividedby R2 is less than the bus voltage. Therefore, D2 is prevented frombearing voltage stress whose magnitude is the bus voltage. When theinput end of the boost power conversion circuit is connected to theinput source, to reduce a circuit loss, S may be controlled to beclosed, so that S short-circuits R1, and a power energy loss caused byR1 can be avoided.

It should be noted that the embodiments corresponding to FIG. 18 to FIG.20 are described by using an example in which the inductor L isconnected to the input positive electrode. It may be understood that,the embodiments corresponding to FIG. 18 to FIG. 20 are also applicableto a case in which the inductor L is connected to the input negativeelectrode. In addition, selection of a type of the controllable switchin FIG. 19 and FIG. 20 is not limited in the embodiments of thisapplication. Refer to a type selection principle of the controllableswitch in the foregoing other embodiments.

Method Embodiment

Based on the boost power conversion circuit provided in the foregoingembodiments, an embodiment of this application further provides a boostpower conversion circuit control method. The boost power conversioncircuit control method is described in detail below with reference tothe accompanying drawings.

FIG. 21 is a flowchart of a boost power conversion circuit controlmethod according to an embodiment of this application.

The boost power conversion circuit control method provided in thisembodiment is applied to the boost power conversion circuit provided inany one of the foregoing embodiments. The method includes the followingoperations.

Operation S210: Determine whether a voltage on an input end of the boostpower conversion circuit is less than a startup voltage of the boostpower conversion circuit, and if yes, perform operation S220, orotherwise, perform operation S230.

In one embodiment, whether the input end is connected to an input sourcemay be determined by measuring the voltage on the input end of the boostpower conversion circuit. When the voltage on the input end is less thana preset voltage value, it indicates that the voltage on the input endis less than the startup voltage of the boost power conversion circuit.Certainly, if a voltage control circuit is automatically triggered, thevoltage on the input end may not need to be measured. When there is noinput source, the voltage control circuit is automatically connected toclamp a voltage. For example, when there is no input source, a state ofa normally-closed relay or contactor is on; and when there is the inputsource, a state is off. How to determine whether the input end isconnected to the input source is not specifically limited in thisembodiment of this application.

Operation S220: When it is determined that the voltage on the input endof the boost power conversion circuit is less than the startup voltageof the boost power conversion circuit, the voltage control circuit makesa voltage borne by the second diode less than a bus voltage of the boostpower conversion circuit.

Operation S230: When it is determined that the voltage on the input endof the boost power conversion circuit is greater than or equal to thestartup voltage, the voltage control circuit stops clamping.

The method provided in this embodiment is applicable to the boost powerconversion circuit. The boost power conversion circuit includes a firstdiode and a second diode that are connected in series, and both thefirst diode and the second diode are freewheeling diodes. When thevoltage on the input end of the boost power conversion circuit is lessthan the startup voltage of the boost power conversion circuit, butthere is a bus voltage on an output end, the first diode and the seconddiode bear the bus voltage in a reverse direction. Therefore, a voltageof a common point of the first diode and the second diode needs to beclamped. The voltage control circuit added in this embodiment of thisapplication may clamp the voltage of the common point of the first diodeand the second diode, and make, when no input source is connected to theinput end of the boost power conversion circuit, the voltage borne bythe common point of the first diode and the second diode less than a busvoltage, so that voltage stress borne by the common point of the firstdiode and the second diode can be reduced, and selection of a diode typeis facilitated.

Based on the boost power conversion circuit and method provided in theforegoing embodiments, the boost power conversion circuit may be appliedto many situations, for example, the photovoltaic power generationfield. Descriptions are provided below by using an example in which theboost power conversion circuit is applied to the photovoltaic powergeneration field.

An embodiment of this application further provides an inverter. FIG. 22is a schematic diagram of an inverter according to an embodiment of thisapplication.

The inverter includes two levels of circuits. One level is the foregoingboost power conversion circuit 2000, that is, DC-DC. The other level isan inverter circuit 3000, that is, DC-AC. The inverter is applied to thephotovoltaic power generation field. To be specific, an input end of theboost power conversion circuit 2000 is connected to a photovoltaiccomponent PV, and is configured to boost and then output an outputvoltage of the photovoltaic component PV to an input end of the invertercircuit 3000. The inverter circuit 3000 inverts a direct current outputby the boost power conversion circuit 2000 into an alternating currentand provides the alternating current to a subsequent-level circuit. Thesubsequent-level circuit may be an alternating-current power network oralternating-current load.

Because a power station in the photovoltaic power generation fieldusually includes a plurality of inverters, output ends of DC-DC in theplurality of inverters are connected in parallel, but due to somereasons, an input end of specific DC-DC is not successfully connected tothe photovoltaic component, and other DC-DCs that are connected inparallel are successfully connected to the photovoltaic component.Because the output ends are connected in parallel, a bus voltage hasalready been set on output ends of the DC-DCs that are connected inparallel, a diode in DC-DC whose input end is not successfully connectedto the photovoltaic component bears a back voltage of the bus voltage.However, if the DC-DC provided in this embodiment of this application isused, the diode that bears the back voltage is protected, thereby makingit easier to select a diode type.

Based on the boost power conversion circuit and method provided in theforegoing embodiments, the boost power conversion circuit may be appliedto many situations, for example, the uninterruptible input source fieldand the photovoltaic power generation field. Descriptions are providedbelow by using an example in which the boost power conversion circuit isapplied to the photovoltaic power generation field.

Embodiment of a photovoltaic power generation apparatus

A photovoltaic power generation apparatus provided in this embodimentincludes a photovoltaic component and the boost power conversion circuitdescribed in any one of the foregoing embodiments. The boost powerconversion circuit and the photovoltaic component are in one-to-onecorrespondence. An input end of the boost power conversion circuit isconnected to the photovoltaic component. The boost power conversioncircuit is configured to boost and then output an output voltage of theconnected photovoltaic component to a subsequent-level circuit.

Embodiment of a photovoltaic power generation system

Based on the boost power conversion circuit and method and thephotovoltaic power generation apparatus provided in the foregoingembodiments, the boost power conversion circuit may be applied to manysituations, for example, the uninterruptible input source field and thephotovoltaic power generation field. Descriptions are provided below byusing an example in which the boost power conversion circuit is appliedto the photovoltaic power generation field.

An embodiment of this application further provides a photovoltaic powergeneration system. The photovoltaic power generation system is describedin detail below with reference to the accompanying drawings.

Specifically, still refer to FIG. 23. The photovoltaic power generationsystem provided in this embodiment includes a photovoltaic component andat least two photovoltaic power generation apparatuses.

Output ends of boost power conversion circuits in all the photovoltaicpower generation apparatuses are connected in parallel. Two photovoltaicpower generation apparatuses are used as an example below fordescription. Correspondingly, two boost power conversion circuits areincluded. As shown in FIG. 23, an output end of a first boost powerconversion circuit 2200 and an output end of a second boost powerconversion circuit 2300 are connected in parallel. Both the output endof the boost power conversion circuit 2200 and the output end of theboost power conversion circuit 2300 are connected to an input end of aninverter circuit 3000.

An input end of each of the boost power conversion circuits is connectedto a corresponding photovoltaic component.

The boost power conversion circuit is configured to boost and thenoutput an output voltage of the connected photovoltaic component to asubsequent-level circuit. An input end of the first boost powerconversion circuit 2200 is connected to a first photovoltaic componentPV1, an input end of the second boost power conversion circuit 2300 isconnected to a second photovoltaic component PV2, the first boost powerconversion circuit 2200 is configured to boost an output voltage of PV1,and the second boost power conversion circuit 2300 is configured toboost a voltage of PV2.

However, in actual application, connections between some photovoltaiccomponents and corresponding boost power conversion circuits may bedisconnected. In other words, a voltage on an input end of the boostpower conversion circuit is less than a startup voltage of the boostpower conversion circuit. In this case, to reduce voltage stress of asecond diode in the boost power conversion circuit, a voltage of thesecond diode needs to be clamped, so that the voltage stress borne bythe second diode is reduced, and selection of a component type isfacilitated.

It may be understood that, after output ends of all boost powerconversion circuits are connected in parallel, the boost powerconversion circuits may be connected to an inverter, and the inverterinverts a direct current into an alternating current and then feeds backthe alternating current to an alternating-current power network oralternating-current load. In addition, after the output ends of all theboost power conversion circuits are connected in parallel, the boostpower conversion circuits may be connected to a direct-current powernetwork or direct-current load.

It should be understood that, in this application, “at least one” meansone or more, and “a plurality of” means two or more. The term “and/or”describes an association between associated objects and represents thatthree associations may exist. For example, A and/or B may indicate thatonly A exists, both A and B exist, and only B exists, where A and B maybe singular or plural. The character “/” generally indicates an “or”relationship between the associated objects. “At least one of thefollowing items” or a similar expression means any combination of theseitems, including a single item or any combination of a plurality ofitems. For example, at least one of a, b, or c may represent a, b, c,a-b, a-c, b-c, or a-b-c, where a, b, and c may be singular or plural.

The foregoing is merely preferable embodiments of the present invention,and does not constitute any limitation on the present invention.Although the present invention is disclosed above by using exampleembodiments, the example embodiments are not used to limit the presentinvention. Any person skilled in the art may make many possiblevariations and modifications to the technical solutions of the presentinvention or change the technical solutions of the present inventioninto equivalent embodiments by using the foregoing method and technicalcontent within the range of the technical solutions of the presentinvention. Therefore, all content within the technical solutions of thepresent invention and any simple modification and equivalent change andmodification made to the foregoing embodiments based on the technicalessence of the present invention fall within the protection scope of thetechnical solutions of the present invention.

What is claimed is:
 1. A boost power conversion circuit, comprising: afirst switching transistor, a second switching transistor, an inductor,a flying capacitor, a first diode, a second diode, and a voltage controlcircuit; wherein the inductor, the first diode, and the second diode aresuccessively connected in series to form a first branch, the firstbranch is connected in series to an input positive electrode and aninput negative electrode of the boost power conversion circuit to form amain circuit, both an anode of the first diode and an anode of thesecond diode are close to the input positive electrode of the boostpower conversion circuit, and both a cathode of the first diode and acathode of the second diode are close to the input negative electrode ofthe boost power conversion circuit; the inductor, the first switchingtransistor, and the second switching transistor are connected in seriesto form a first closed loop, and the first switching transistor, thesecond switching transistor, the first diode, and the second diode forma second closed loop; and one end of the flying capacitor is connectedto a common point of the first diode and the second diode, and the otherend of the flying capacitor is connected to a common point of the firstswitching transistor and the second switching transistor; and thevoltage control circuit is connected in series in a third closed loop,the third closed loop is a loop comprising the inductor, the firstswitching transistor, the flying capacitor, the second diode, the inputpositive electrode, and the input negative electrode, the voltagecontrol circuit is configured to make a voltage borne by the seconddiode less than a bus voltage of the boost power conversion circuit, andthe bus voltage is a voltage difference between a positive bus voltageand a negative bus voltage; or a first end of the voltage controlcircuit is connected to a common end of the first diode and the seconddiode, a second end of the voltage control circuit is connected to areference point, the reference point is used to provide a clampingpotential, and the clamping potential is between a negative buspotential and a positive bus potential; and the voltage control circuitis configured to clamp a voltage of the common point of the first diodeand the second diode when a voltage on an input end of the boost powerconversion circuit is less than a startup voltage of the boost powerconversion circuit.
 2. The boost power conversion circuit according toclaim 1, wherein when the voltage control circuit is connected in seriesin the third closed loop, the voltage control circuit comprises one of aclamping diode, a controllable switching transistor, and a compoundcomponent; and the compound component comprises the clamping diode andthe controllable switching transistor that are connected in parallel. 3.The boost power conversion circuit according to claim 2, wherein whenthe voltage control circuit comprises the controllable switchingtransistor or comprises the compound component, the voltage controlcircuit further comprises a controller; and the controller is configuredto: when the voltage on the input end of the boost power conversioncircuit is less than the startup voltage of the boost power conversioncircuit, control to open the controllable switching transistor; and thecontroller is further configured to: when the voltage on the input endof the boost power conversion circuit is greater than the startupvoltage of the boost power conversion circuit, control to close thecontrollable switching transistor.
 4. The boost power conversion circuitaccording to claim 2, wherein when the voltage control circuit comprisesthe clamping diode, the voltage control circuit further comprises afirst resistor and a second resistor; the first resistor is connected inparallel between two ends of the clamping diode; and the second resistoris connected in parallel between two ends of the second diode.
 5. Theboost power conversion circuit according to claim 2, wherein when thevoltage control circuit comprises the compound component, the voltagecontrol circuit further comprises a first resistor and a secondresistor; the first resistor is connected in parallel between two endsof the clamping diode; and the second resistor is connected in parallelbetween two ends of the second diode.
 6. The boost power conversioncircuit according to claim 2, wherein when the voltage control circuitcomprises the controllable switching transistor, the voltage controlcircuit further comprises a controller, a first resistor, and a secondresistor; the controllable switching transistor is connected in seriesbetween the first diode and the second diode; the first resistor isconnected in parallel between two ends of the controllable switchingtransistor; and the second resistor is connected in parallel between twoends of the second diode.
 7. The boost power conversion circuitaccording to claim 1, further comprising a first bus capacitor and asecond bus capacitor; wherein the first switching transistor, the secondswitching transistor, the first diode, the second diode, the first buscapacitor, and the second bus capacitor form a second closed loop, andthe reference point is a common point of the first bus capacitor and thesecond bus capacitor.
 8. The boost power conversion circuit according toclaim 1, further comprising a first bus capacitor, a second buscapacitor, a third bus capacitor, and a fourth bus capacitor; whereinthe first switching transistor, the second switching transistor, thefirst diode, the second diode, the first bus capacitor, the second buscapacitor, the third bus capacitor, and the fourth bus capacitor form asecond closed loop, and the reference point is any common point betweenthe first bus capacitor, the second bus capacitor, the third buscapacitor, and the fourth bus capacitor.
 9. The boost power conversioncircuit according to claim 7, wherein the voltage control circuitcomprises a third switching transistor and a controller, a first end ofthe third switching transistor is connected to the common end of thefirst diode and the second diode, and a second end of the thirdswitching transistor is connected to the reference point; and thecontroller is configured to: when the voltage on the input end of theboost power conversion circuit is less than the startup voltage of theboost power conversion circuit, control to close the third switchingtransistor; and the controller is further configured to: when thevoltage on the input end of the boost power conversion circuit isgreater than the startup voltage of the boost power conversion circuit,control to open the third switching transistor.
 10. The boost powerconversion circuit according to claim 7, wherein the voltage controlcircuit comprises a third diode, a cathode of the third diode isconnected to the common point of the first diode and the second diode,and an anode of the third diode is connected to the reference point. 11.The boost power conversion circuit according to claim 1, wherein thatthe inductor, the first diode, and the second diode are successivelyconnected in series to form the first branch and the first branch isconnected in series to the input end of the boost power conversioncircuit to form the main circuit includes: a first end of the inductoris connected to the input positive electrode, and a second end of theinductor is connected to the first diode and the second diode that aresuccessively connected in series.
 12. The boost power conversion circuitaccording to claim 1, wherein that the inductor, the first diode, andthe second diode are successively connected in series to form the firstbranch and the first branch is connected in series to the input end ofthe boost power conversion circuit to form the main circuit comprises: afirst end of the inductor is connected to the input negative electrode,and a second end of the inductor is connected to the first diode and thesecond diode that are successively connected in series.
 13. A boostpower conversion circuit control method, applied to the boost powerconversion circuit, the boost power conversion circuit comprising: afirst switching transistor, a second switching transistor, an inductor,a flying capacitor, a first diode, a second diode, and a voltage controlcircuit; wherein the inductor, the first diode, and the second diode aresuccessively connected in series to form a first branch, the firstbranch is connected in series to an input positive electrode and aninput negative electrode of the boost power conversion circuit to form amain circuit, both an anode of the first diode and an anode of thesecond diode are close to the input positive electrode of the boostpower conversion circuit, and both a cathode of the first diode and acathode of the second diode are close to the input negative electrode ofthe boost power conversion circuit; the inductor, the first switchingtransistor, and the second switching transistor are connected in seriesto form a first closed loop, and the first switching transistor, thesecond switching transistor, the first diode, and the second diode forma second closed loop; and one end of the flying capacitor is connectedto a common point of the first diode and the second diode, and the otherend of the flying capacitor is connected to a common point of the firstswitching transistor and the second switching transistor; and thevoltage control circuit is connected in series in a third closed loop,the third closed loop is a loop comprising the inductor, the firstswitching transistor, the flying capacitor, the second diode, the inputpositive electrode, and the input negative electrode, the voltagecontrol circuit is configured to make a voltage borne by the seconddiode less than a bus voltage of the boost power conversion circuit, andthe bus voltage is a voltage difference between a positive bus voltageand a negative bus voltage; or a first end of the voltage controlcircuit is connected to a common end of the first diode and the seconddiode, a second end of the voltage control circuit is connected to areference point, the reference point is used to provide a clampingpotential, and the clamping potential is between a negative buspotential and a positive bus potential; and the voltage control circuitis configured to clamp a voltage of the common point of the first diodeand the second diode when a voltage on an input end of the boost powerconversion circuit is less than a startup voltage of the boost powerconversion circuit; wherein the method comprises: when it is determinedthat a voltage on an input end of the boost power conversion circuit isless than a startup voltage of the boost power conversion circuit,controlling, by the voltage control circuit, a voltage borne by thesecond diode to be less than a bus voltage of the boost power conversioncircuit, wherein the bus voltage is a voltage difference between apositive bus voltage and a negative bus voltage.
 14. An inverter,comprising an inverter circuit and the boost power conversion circuit,the boost power conversion circuit comprising: a first switchingtransistor, a second switching transistor, an inductor, a flyingcapacitor, a first diode, a second diode, and a voltage control circuit;wherein the inductor, the first diode, and the second diode aresuccessively connected in series to form a first branch, the firstbranch is connected in series to an input positive electrode and aninput negative electrode of the boost power conversion circuit to form amain circuit, both an anode of the first diode and an anode of thesecond diode are close to the input positive electrode of the boostpower conversion circuit, and both a cathode of the first diode and acathode of the second diode are close to the input negative electrode ofthe boost power conversion circuit; the inductor, the first switchingtransistor, and the second switching transistor are connected in seriesto form a first closed loop, and the first switching transistor, thesecond switching transistor, the first diode, and the second diode forma second closed loop; and one end of the flying capacitor is connectedto a common point of the first diode and the second diode, and the otherend of the flying capacitor is connected to a common point of the firstswitching transistor and the second switching transistor; and thevoltage control circuit is connected in series in a third closed loop,the third closed loop is a loop comprising the inductor, the firstswitching transistor, the flying capacitor, the second diode, the inputpositive electrode, and the input negative electrode, the voltagecontrol circuit is configured to make a voltage borne by the seconddiode less than a bus voltage of the boost power conversion circuit, andthe bus voltage is a voltage difference between a positive bus voltageand a negative bus voltage; or a first end of the voltage controlcircuit is connected to a common end of the first diode and the seconddiode, a second end of the voltage control circuit is connected to areference point, the reference point is used to provide a clampingpotential, and the clamping potential is between a negative buspotential and a positive bus potential; and the voltage control circuitis configured to clamp a voltage of the common point of the first diodeand the second diode when a voltage on an input end of the boost powerconversion circuit is less than a startup voltage of the boost powerconversion circuit; wherein the boost power conversion circuit isconfigured to boost and then output a received voltage to an input endof the inverter circuit; and the inverter circuit is configured toinvert, into an alternating current, a direct current output by theboost power conversion circuit.